You should check the ABS module on your rear brakes first. The ABS module can be checked with a multimeter. A Chilton's Auto repair manual will tell you what the correct ohms reading range is for a good module. I had the module changed at a reputable auto repair shop, not a Ford Dealership and it worked fine. My ABS light would come on my Windstar after I reached speeds of about 55 mph. It would reset after ignition shutoff/startup. My light is coming on again after about three years and my guess is that another ABS module has failed on the other three wheels.
I hope this posting helps, please let me know!
Mark
